The field of the invention is polyamide adhesives for textiles and the invention is particularly concerned with powdered mixtures of polyamides for heat sealing textiles by the powder point process.
The state of the art of methods and apparatus for depositing powdered thermoplastic adhesive materials on the outer surface of textiles may be ascertained by reference to U.S. Pat. Nos. 4,139,613, 4,183,978 and 3,667,422 and British Pat. No. 1,295,558, the disclosures of which are incorporated herein.
Copolyamides useful as adhesives and the state of the art thereof may be ascertained by reference to U.S. Pat. Nos. 2,252,555; 3,515,702; 3,839,121; 3,883,485; 3,883,487; 3,948,844; 3,950,297; 4,035,436; 4,046,747; 4,101,534 and Re. 27,939; British Pat. Nos. 1,458,640 and 1,548,431 and West German Published Application Nos. 24 36 430 and 28 06 933, the disclosures of which are incorporated herein.
The state of the prior art of producing polyamide powders may be ascertained by reference to U.S. Pat. No. 4,143,025 and the Kirk-Othmer "Encyclopedia of Chemical Technology", 2nd ed., vol. 16 (1968) under the section "Polyamide (Plastics)", pages 88-105, particularly page 92-polylauryllactam (nylon-12), and polyundecanamide (nylon-11), page 101, Solution Processes, and Powder Processing, pages 101-102, the disclosures of which are incorporated herein.
According to British Pat. No. 1,295,558, the spot coating of interlinings for textiles is carried out mainly by three methods:
1. A suitable plastic powder, for example, a polyamide or polyethylene based powder, is applied by a doctor blade to an engraving roller having recesses in the form of dots disposed in an even raster or grid formation and having a diameter of about 1 mm so that the plastic powder fills the recesses. The web of the interlining, which has been preheated to a high temperature by means of heating rollers, is passed around the engraving roller under tension and the plastics powder is transferred from the recesses to the web of interlining material (Powder point or powder dot coating process).
2. A network of spots of a suitable plastic, such as polyethylene, is prepared in the form of a raster, the spots being interconnected by very fine webs. The network is applied dry to the hot interlining, the fine webs breaking up and disappearing, and the spots of the plastic fusing to the interlining. Interlinings of this kind have a relatively hard handle and can be fixed only on relatively heavy facing materials and the plastics also tend to bleed through and stick to the fixing press.
3. In the least expensive and least complex process, suitable plastics, such as PVC, polyamide or polyethylene, are mixed with plasticizers or in aqueous or solvent-containing media to form pastes which are printed by means of a printing roller formed with perforations arranged as a raster (paste printing process).
The use of copolyamides as synthetic resin adhesives for laminating fabrics has been known for a long time as disclosed in U.S. Pat. No. 2,252,555 at page 3, Column 2, lines 42-50. Lauryllactam based synthetic resin adhesives have been used especially commercially in recent years for heat sealing textiles as disclosed in U.S. Pat. No. 3,515,702 and U.S. Pat. No. Re. 27,939. These synthetic resin adhesives are not yet fully satisfactory as regards their resistance to hot water and cleaning and as a result of unsatisfactory performance, many variations have been introduced. Thus, U.S. Pat. No. 3,839,121 discloses synthetic resin adhesives based on copolyamides which contain branched chain diamine components with improved resistance to cleaning but bonding at higher temperatures is required. Nonamethylenediamine based copolyamides also exhibit too high a melting point and therefore are not suitable as synthetic resin adhesives for heat sealing textiles as disclosed in British Pat. Nos. 1,458,640 and 1,548,431. Copolyamides with low melting points are unsatisfactory with respect to their hot-water resistance and their fasteness to cleaning, as disclosed in U.S. Pat. Nos. 3,883,485; 3,883,487; 3,948,844 and 3,950,297 and German Published Application Nos. 24 36 430 and 28 06 933. Previously mentioned U.S. Pat. No. 2,252,555 further discloses that copolyamides when mixed with homopolyamides are especially suitable for bonding metal surfaces (loc. cit., Column 1, lines 1-10). The same teaching is found in U.S. Pat. No. 4,101,534, beginning at the top of Column 2.
U.S. Pat. No. 3,035,436 teaches the use of mixtures of crystalline homopolyamides or copolyamides of lauryllactam and of 11-aminoundecanoic acid in specific proportions in a mixture with crystalline homopolyamides or copolyamides of hexamethylenediamine and 1,12-dodecanoicdicarboxylic acid for bonding metals, these mixtures also being suitable for use in powder form. In this case, however, when copolyamides are used, they contain at most 5 or 10% by weight of other copolyamide forming basic components. Accordingly, the use of crystalline homoamides or copolyamides is required.
These mixtures are used especially in the form of films for sealing the corner joints of cans. U.S. Pat. No. 4,035,436 teaches that good bonding of the synthetic resin adhesive for high temperatures and especially for good water resistance is achieved only when the mixtures exhibit high crystallinity. Only then is it possible to operate with melt cooling cycles which are extremely short.
The conditions for bonding textiles using the powder point process are entirely different from the prior art uses of polyamide adhesives. By powder point process or powder dot coating process is meant the process especially described in U.S. Pat. No. 3,667,422 and described as method 1 of British Pat. No. 1,295,558. No short cycle periods are needed in the ironing presses and on the other hand, bonding is desired within a wide temperature range. The adhesive must wet the fabric as thoroughly as possible and must be satisfactorily resistant to hot detergent liquors and chemical cleaning agents. Only very low bonding temperatures are allowed for delicate fabrics. Therefore, a melting range having an upper limit of 135.degree. C. should not be exceeded. These requirements cannot be met when the mixtures described in U.S. Pat. No. 4,035,436 are used.
U.S. Pat. No. 2,698,966 further discloses the use of mixtures of powdered homopolyamides for the manufacture of molded articles, where a molded article is first pressed from the powder mixture and then the pressed article is sintered at a higher temperature.
U.S. Pat. No. 2,698,966 offers no indication of how powdered mixtures of copolyamides can be used for the hot sealing of textiles by the powder point process.